1. Observation: They observe the star from two different points in Earth's orbit around the Sun, typically six months apart. This creates a baseline of about 300 million kilometers.
2. Angular Measurement: They measure the apparent shift in the star's position against the background of distant stars. This shift is called the parallax angle. The closer the star, the larger the parallax angle.
3. Calculation: The distance to the star is calculated using a simple trigonometric formula that relates the parallax angle, the baseline distance, and the distance to the star.
The parallax method is based on the principle of triangulation, a fundamental technique in geometry and surveying.
Example:
If the parallax angle of a star is 0.1 arcseconds, the distance to the star can be calculated as:
Distance (in parsecs) = 1 / Parallax angle (in arcseconds)
In this case, the distance to the star would be 10 parsecs, which is approximately 32.6 light-years.
Limitations:
The parallax method is effective for stars within a few hundred light-years. Beyond that distance, the parallax angles become too small to measure accurately. Other methods, such as standard candles and redshift, are used for more distant stars.
